Disk slots for supplying cooling air into turbine blades have an enlarged cross-sectional flow area adjacent an inlet end, and a reduced cross-sectional flow area at downstream locations. In this manner, pressure losses associated with the inlet end of the disk slot are reduced.
Gas turbine engines are known, and operate to supply propulsion for various applications. In a typical gas turbine engine, a fan section delivers air to a compressor section. Air is compressed in the compressor section, and mixed with fuel in a combustor section. Products of combustion are directed downstream over turbine blades, and drive turbine blades and associated rotors to rotate.
One challenge facing the turbine section, is that the blades are subject to very hot temperatures. Thus, cooling air is typically supplied to passages within the blades, and may be directed outwardly of openings in the blades and into the combustion flow stream. To drive the cooling air through the blade and into the combustion air stream, the cooling air must be at a relatively high pressure. In particular, the pressure of this cooling air must exceed the pressure of the hot gas flowing around the contour of the turbine blade.
Typically, the turbine section includes a plurality of rotors each having a plurality of disk slots at spaced circumferential locations. The rotors may be provided with disk lugs, or a plurality of ears. The turbine blades are inserted into these slots, with mating structure received between the disk lugs. The disk slot includes a cooling air supply space radially inwardly of a radially innermost end of the turbine blade. Openings in a radial bottom of the turbine blade communicate with cooling air in the disk slot. Air flows from the compressor section, around the combustor section, into the disk slots, and upwardly into these blade openings to be delivered to the turbine blades.
The size of the disk slots has been limited in practice. In particular, structural considerations must be taken into account, as the disk lugs must support the turbine blades, and thus are subject to stresses and applied centrifugal forces. The bottom of the disk slot forms what is known as a disk live rim. This area carries what are known as disk hoop loads, and is an important consideration in the disk structural design.
For cooling requirements alone, it might be desirable to make the disk slot as large as possible to reduce the flow velocity of the air, thereby minimizing pressure losses of the cooling air delivered to the turbine blade. However, the structural considerations mentioned above limit the size of the disk slot.
The pressure losses are highest at the inlet of the slot. This is due to what is known as an “entrance effect” coupled with the fact that all of the cooling air must pass through this region, creating a highest flow velocity along the slot. The pressure losses tend to decrease along the length of the slot as the passage friction tends to be a smaller loss driver than the entrance effect. Also, the flow velocity is reduced as cooling air is bled off into successive passages in the turbine blades.
In the prior art, while there have been curved air flow slots, in general, the cross-sectional area has been relatively constant along a flow length.
In sum, it would be desirable to reduce pressure losses within the disk slot, and in particular at the inlet portion of the disk slot.